Conventionally, an optical determination apparatus has been provided which includes, in order to improve the accuracy of determination of whether or not granules are conforming or nonconforming, transfer means for transferring a material, optical detection means with a light source section that irradiates the material transferred by the transfer means with light with a plurality of wavelengths and an image pickup section that picks up an image of reflected light and/or transmitted light from the material, and determination means for determining the material by comparing density values at two wavelengths in image pickup data taken by the optical detection means with threshold areas of predetermined density values at the two wavelengths (Patent Literature 1). In the optical determination apparatus, when the determination means sets the threshold areas, the image pickup section picks up an image of reflected light and/or transmitted light from a material sample to be determined which has been transferred by the transfer means, the determination means draws density values at any two wavelengths in the image pickup data, on a two-dimensional graph, determines, for all pixels with the respective density values drawn on the two-dimensional graph, whether or not a circle between two points with a diameter defined by those of the pixels which are located at two different points contains any pixel other than the pixels at the two points, joins the pixels at the two points with a connection line only when the determination indicates that the circle between two points contains no pixel other than the pixels at the two points, and sets a closed area drawn by joining such connection lines together to be the threshold area.
In the optical determination apparatus disclosed in Patent Literature 1, the outer shapes of the threshold areas set by the determination means are accurately defined so as not to include a determination area. The optical determination apparatus is thus advantageously effective in that the threshold areas allow the material to be determined and in that sorting based on the determination is also accurate.
However, to simplify an enormous amount of complicated information (a CCD camera serving as the image pickup section in Patent Literature 1 enables, for each of colors, red, green, and blue, 256 types of hues to be distinguished from one another for 8 bits, thus allowing a total of as many as 16,777, 216 types of colors to be distinguished from one another for three-dimensional RGB color space information), the optical determination apparatus disclosed in Patent Literature 1 plots the density value for each of the colors, red, green, and blue acquired by the CCD camera on each of two-dimensional graphs including a red (X axis)-green (Y axis) two-dimensional graph, a green (X axis)-blue (Y axis) two-dimensional graph, and a red (X axis)-blue (Y axis) two-dimensional graph to acquire three-dimensional RGB color space information based on the three two-dimensional graphs.
Acquiring three-dimensional RGB color space information based on the two-dimensional graphs is advantageous when a signal algorithm is very simple and an enormous amount of complicated information is handled. However, since information on two-dimensional planes is observed based on the two-dimensional graphs, a sensitivity setting is disadvantageously limited. Furthermore, not all pieces of RGB color space information can be simultaneously handled, and thus, the above-described optical determination apparatus is disadvantageously not efficient.